Abstract
Pond apple (Annona glabra L.), a tree species native to wetlands of the Americas, including south Florida, may have potential as a flood-tolerant rootstock for commercial Annona species. In pond apple's native wetland soil, Fe[sup+] is reduced to Fe[sup+] which is readily absorbed by plants. In nonflooded, calcareous soils of south Florida, pond apple trees often exhibit symptoms of Fe deficiency. Therefore, the effects of Fe application on plant nutrition and growth of pond apple were studied under flooded and non-flooded conditions. Trees were grown in Krome very gravelly loam soil and fertilized with 0, 0.625, 1.25, 2.5, or 5.0 g/plant of chelated (Sequestrene-138, Fe-EDDHA) or non-chelated (FeSO[sub4]) Fe under flooded or nonflooded conditions. Trees that survived 12 weeks of flooding exhibited morphological adaptations to flooding, such as development of adventitious roots and hypertrophied stem lenticels. Flooding decreased the concentration of N, P, K, Ca, Mg, Zn, and Cu, and increased the concentration of Fe and Mn in the leaves. For non-flooded trees, addition of chelated Fe to the soil resulted in a higher leaf chlorophyll index and more growth compared to trees fertilized with non-chelated Fe. The optimum amount of chelated Fe needed to achieve maximum growth in non-flooded trees was 2.5 to 5 g per plant. For flooded trees, the form of Fe did not affect leaf chlorophyll index and growth. To avoid Fe stress when the soil is not flooded, the use of pond apple as a flood-tolerant rootstock will require considerably higher rates of chelated Fe than the amount applied to traditional Annona rootstocks.
